


Not Weak

by LazySintastic13 (EmeraldWriter)



Category: Undertale (Video Game)
Genre: Alpha/Beta/Omega Dynamics, Alpha/Omega, Alternate Universe - Underfell, M/M, Mating Cycles/In Heat, Multiple Orgasms, Overstimulation, Porn with Feelings, Porn with some plot, Underfell Sans, kustard - Freeform, no knotting, sorry fam
Language: English
Status: Completed
Published: 2017-07-09
Updated: 2017-07-09
Packaged: 2018-11-29 17:56:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,363
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11446050
Author URL: https://archiveofourown.org/users/EmeraldWriter/pseuds/LazySintastic13
Summary: Red is an Omega in heat. And he refused to submit to anyone. Maybe Sans can change his mind.Oh wait, but Sans is also ...Well then. That'll be interesting.(Bad at Summaries, Spare me ><)





	Not Weak

**Author's Note:**

  * For [EchoSol](https://archiveofourown.org/users/EchoSol/gifts).



> I barely made it but here you go! 
> 
> Happy Birthday! :D

_Shit. Shit shit shit shit._ Red clutched to his chest, his breathing coming out as soft pants. His legs trembled, barely able to keep him standing and he struggled to move. The only good thing in this at least was that he was close to his dorms.

As long as he doesn’t bump into anyone on the way, he can take his suppressor pills, and go to bed to sleep it off.

 _Just a little more._ Cheeks tinted red, the skeleton could feel embarrassment well up inside of him when his magic solidified below, and he could feel his slick trickle down his femurs. _Fucking hell._

He heard his phone ring, and promptly ignored it because there wasn’t anything more important than the trek he was currently doing. The ringing was incessant until it finally stopped, and a different sound followed up. A message.

Well, whoever the fucker was bothering him would have to wait, because Red had no fuck’s to give until his heat was over.

Red gritted his teeth, each step were agonizing. His instincts were telling— _screaming_ at him to find a partner to mate with; to be _bred_. In truth, the skeleton was fine with being an omega. Though only a handful of people knew of it for he didn’t seem to be the submissive type. He didn’t act like your normal omega. Gentle, sweet and caring, he was anything but. He was an asshole, this he knew well.

But that wasn’t his issue with being an omega.

His issue bore from the utter embarrassment he feels when he becomes submissive during his heats. To be so dependent and needy brought about a complex feeling of humiliation towards his pride and the sense of wanting to be adored and pampered. He blamed the latter on his biological aspect as an omega than on his actual wants.

His instincts can go fuck itself, because there was no way in hell Red was ever going to believe he _wants_ to be treated like a princess. It was lies. All fucking lies, and being in heat was nothing more than a show of weakness—a vulnerability he could go without.

Promptly unlocking the door, Red, for the first time in his painful journey towards here, sighed in relief that he made it all the way without meeting anyone. He’d be able to lock the door, and then text his roommate to fuck elsewhere during his heat.

But nothing was ever that simple.

Just as he opened the door, he was immediately bombarded with pheromones. Worst of all, it was from an _alpha_ —his roommate.

Red’s legs gave up as his magic immediately reacted to the scent, and his whole body ached to be touched. “ _S-Sans_.” He managed to heave out, sweating bullets and feeling his magic lubricate him more.

“F-Fuck, Red.” Sans sat on the edge of the bed, a hand on his cock already dripping profusely with precum whilst still wearing clothes. The sweat marks were evident on them, but the skeleton hadn’t cared. Taking care of his heat was more important.

Sans gave him a troubled smile. “I-I was calling you. Wanted to warn you a-about my heat.” And then he took a whiff in the air. Sans’ eye lights narrowed as he zeroed in on the other. Red was in his heat too. _Shit._

 _Godamnit._ The scent was so thick; he could taste it in his mouth—sweet like strawberries. Red hated the world then and there. Contrary to always eating mustard, there were exceptions when it comes to wanting anything sweet. He fucking loved strawberries.

But out of all the people, it had to be Sans who’d see him at his weakest. The very monster he deemed to be his rival as they clashed in opinions and ideas. The very monster that both aggravates and confusingly turns him on. The very monster he now lunged at, with energy he never knew he still had, and was now on the other’s lap with their tongues now lathering each other’s.

Arms wrapped around Red’s hips, as his own were around Sans’ neck. Red felt delirious doing something like this. While he was an asshole, yes, he was also a virgin. He had no fucking idea what he was doing; let alone what he needed to do.

They finally parted when Red pulled away to catch his breath. _Fuck._ He didn’t think Sans would be good at kissing. Red’s lack of experience showed in that department.

But he was in charge. He held the reigns. Like hell he was going to be submissive.

He was an omega, sure, but he was still Red; foul-mouthed, crude, rude, with his dark-ass humour, and cynical attitude.

“I-If you’re,” _Damnit, he was stuttering_. Though, it didn’t seem to bother the other at all. In fact, Sans was completely focused on him. And he rather liked the predatory and almost dangerous look in them. A side he had yet to see of his rival. Red licked his mouth and swallowed to speak better. “If you’re not gonna fuck me until I can’t move for weeks, then get the fuck out.”

The hold around him tightened and Sans let a soft chuckle. “Says the one who was all over me.”

Red would’ve growled at that statement, but he ended up taken aback when Sans suddenly bore a dark and serious expression. Red’s soul thumped hard against his chest in … anticipation. Stars, the games he was playing.

“If we do this … I’m not gonna you let go.”

Red was sure his whole face was the colour of his name when a soft gasp escaped his mouth and lower area produced more slick at the declaration. Apparently, his body was amiable to the declaration.

“And I can get pretty … rough and possessive.”

Sans really had quite the self-control. Red was sure the other could feel their shorts dampen from his fluids, and the skeleton refused to check; especially when Red was sure to see the other’s cock in the process. The damn thing was still poking him after all.

“ _Red_.”

 _Stop saying my name_ like _that. Don’t say my name at all._

“Red,” Sans placed a hand on Red’s cheek, gentle and sweet, contrary to his statement earlier. “Are you okay with me? I know we clash a lot, and annoy each other to no end … but I like you, Red. And I don’t want this to be the reason we break.”

 _… Damnit. Damn you._ Tears began to trickle out of Red’s eye sockets and stream down his cheeks. “Y-You romantic sap. Bringing f-feelings into this. Can’t just b-be a quick fuck, huh.”

Red was angry, but towards what? He didn’t know. He really didn’t.

“Sorry.” Sans leaned forward to plant a chaste kiss. “Just ‘cuz we’re both in our heats, doesn’t mean I just wanna take you to bed and fuck you.”

Red had to snort at that, causing Sans to smile. “I just can’t do that kind of thing. I want to be able to treasure my partner.”

_… Stop. Stop lying. Stop it._

“I’m not lying.”

Red jolted. He didn’t realize he said that out loud.

“I’ll say it again. I like you … probably even more than I think I do.” He mumbled that last part, but it still had Red’s eye sockets widening.

But all in all, he was still Red; currently in heat, currently horny, and _not a submissive._

“What? You want some heartfelt lovey-dovey confession? Is that it?”

“Wha—”

“You want me swooning and wrapped around your little finger?”

“That’s no—”

“Do you want me to _belong_ to you?”

Sans gasped when those red eyes felt like it pierced his soul.

 “Wreck me _first_ , then we’ll see.”

And what kind of rival was he if Sans backed down from a challenge. Sans growled, noting the look of anticipation on the other’s face when he did so. “You said you didn’t want to be walking for a week, right?” He grinned widely, showcasing fangs he rarely revealed. “I can _make_ that promise.”

* * *

 

_Shit. Shit shit shit shit._

Sans groaned when he thrusted in deep, coming inside to coat the inner walls wrapped around him again in blue. The sensation made Red whimper as he came as well; his juices drenching Sans’ cock and the sheets beneath for the umpteenth time. Toes involuntarily curled in and Red felt his insides convulse continuously and uncontrollably around Sans from the overstimulation.

 “S-Sans.” Red’s voice, normally loud, were nothing more than breathless whispers. “S-Slow— _nnghhh_.” He gritted his teeth as Sans didn’t relent in letting up on the brutal pace that’d been set.

 _No. No no nononono._ He refuse. He’s not. He’s not weak. He’s not—“ _Aaagh! Fuck, Sans!”_ He harshly whispered and hissed when he felt his clit rubbed. No doubt his body shook, doubtful he had any energy to resist the onslaught of both pleasure and pain done onto him, and yet, he still wanted more.

Sans never said a word throughout it all, only groaning and panting heavily, all his focus was on making Red come over and over and over again.

Red whimpered and mewled at the treatment, tears pouring from sockets as hands clutched tightly onto the mattress. He stiffened, back arching and head turning to a side with a gasp—another orgasm hitting him, no less powerful than the others. And Red hated that he enjoyed every single one of it.

He was an absolute wreck, both physically and mentally. He couldn’t control being the greedy omega in him. A side he outright denied its existence, because he didn’t want to be seen like this.

“Red.” Hearing the deep and thick voice caused the said skeleton to look at Sans in the eyes, albeit blurrily from the tears, “You’re so beautiful and strong.”

Red would never admit that he felt happy at hearing the praise. Instead, he growled, appearing to intimidate but fell short due to the fact that Sans _was still moving_.

But his expression was enough for Sans to elaborate. “Don’t you realize how strong you are? How much power you actually have?”

Sans pulled the pliant and still shaking body so that Red was seated on his lap. Only then did Sans stopped moving to speak and place kisses on his partner’s clavicle and neck. “Don’t you know how much power you have over me? What you do to me?”

Red held his breath when he saw blue eye lights meet his gaze. “You can practically make me do anything, I’d do it.”

Red was in disbelief, it was hard to believe. Did he have … that much power? His hands slowly lifted and placed them on his partner’s cheeks. “… Y-You …” he swallowed and took a moment to try again. “… You b-belong to … me?”

That seemed to be the trigger, and Red gasped loudly when Sans began thrusting his hips. “Yes. _Yes, I do._ ”

Their mouths met and tongues meshed before Sans pulled away. “You have me.”

And the intense gaze hit Red hard. He leaned down to mash their mouths again, his hips moving on their own.

“You’re mine.” Red growled, panting heavily as he bit Sans’ clavicle.

“ _Yes._ ” Sans hissed, and their pace only got rougher and faster.

Bones harshly met with loud clacks. Other than the groans, gasps and heavy rapid pants from both skeletons, it was also hard to ignore the loud squelching noises that seem to echo in their ears.

 _“Fuck_ , Sans. _Sans_.” Red keened, his hold tightening around the other as another orgasm was wrung out of him.

“Shit, _Red._ ” Hot walls squeezed him—milking him to cum, and Sans spurted inside Red once more.

 _Stars_ , Red felt so bloated. But the two stopped to catch their breaths.

Their heat seemed to have subsided too, but only enough for their thoughts to be unclouded by desires; however, their bodies still ached for more release. Fucking heat.

It was insatiable.

Red chuckled weakly, his throat dry, “H-How many does that m-make it?”

They’ve lost count. Sans shrugged. “Beats me.”

“Heh,” Red couldn’t help laughing. He probably looked insane but he didn’t care.

Sans was confused at what brought it up, but he just smiled. He rather enjoyed hearing the other laugh so freely, and actually happy.

Red wiped away his tears when he eventually dissolved to soft chuckles until he sighed in content, and placed his forehead against Sans’. His face was probably tear-stained too but he was too tired to care about that.

“I’m still shaking.” He said, grinning all the while, causing the latter to snort. “I don’t think I'm going to able to walk … for _months_.”

“Pfft. You’re exaggerating.” He kissed Red softly. “You’ll be fine in a couple of days.”

Red hummed and a peaceful silence settled in.

“… So,” Red started, looking away.

“Hmm?”

“We’re a … We’re a thing now?”

Sans felt his heart get stuck on his throat, but he forced himself to speak, taking a deep breath. “We … don’t have to be.”

“What? … But didn’t you—”  

“I know … But I don’t want to force you.”

“… You confusing _indecisive_ fuck.” Red bared his teeth, stunning the other at the aggression. “You don’t get to instil _feelings_ in me, and not take responsibility for it. But _fine_ you fuck, I’ll do what I want. We are dating and that is that. _Capiche?_ ”

Sans was rendered speechless for several moments, and his silence was only making Red’s mood worsen by the second. Though, when he finally decided to answer, what came out of his mouth was, in Red’s opinion, an insufferable laugh and not at all cute and endearing to hear.

“Oh stars,” He kissed Red on the mouth, and then his cheeks and nose. “Yeah. Hehe. Capiche.” Red was just too strong for him.

The other skeleton ignored the heat that no doubt made his cheeks flush and coughed. “G-Good.”

Suddenly, both skeletons felt a jolt trail down their spine.

Right.

They were still in the middle of their heat session.

Red grinned widely, “Now that’s settled, more fucking, less talking.” He grinded his pelvis against Sans’, causing the grip on his hip bones to tighten.

“Yeah,” Sans licked his mouth. “ _Let’s_.”

**Author's Note:**

> Hoped you liked it! ^^")


End file.
